Adaptation protocols for local peer group (LPG) networks in dynamic roadway environments

ABSTRACT

A method and system for determining a size of a local peer group (LPG) network in a dynamic roadway (mobile) environment is provided. In one embodiment, the method comprises measuring a roundtrip time between a first node and a second node, and utilizing the measured roundtrip time to select the size of the local peer group network from a lookup table. In another embodiment, the method comprises determining when the roundtrip time exceeds a time interval of the heartbeat signal, and when the roundtrip time exceeds the time interval of the heartbeat signal adjusting the size of the local peer group network.

BACKGROUND

The present invention relates generally to wireless mesh networks, andmore particularly to adaptation protocols for mesh networks in dynamicroadway environments.

A wireless mesh network is a communications network made up of radionodes organized in a mesh topology. In a full mesh topology, each nodeis connected directly to each of the other nodes. In a partial meshtopology, nodes are connected to only some, not all, of the other nodes.The coverage area of the radio nodes working together as a singlenetwork is sometimes known as a mesh cloud. Wireless mesh networks canbe implemented via various wireless standards, including 802.11, 802.16,and cellular technologies.

A mesh network provides the advantage of many-to-many connectionsbetween nodes, i.e., there is usually more than one possible route forcommunicating information between nodes. Mesh networks are also capableof dynamically updating and optimizing these connections. As new nodesbecome available they may be added to the mesh network. Nodes may alsobe removed from the mesh network. Thus, the topology of a mesh networkis dynamic.

The nodes that form a mesh network may be highly mobile. For example,radio nodes may be part of an automobile or another type of motorvehicle that is constantly changing position. These nodes constantlyroam (change position) within the mesh network. In addition, the sizeand topology of a mobile mesh network is constantly changing as nodesmove in and out of a coverage area. The topology of a mobile meshnetwork changes even more frequently than the topology of a stationarymesh network.

Thus, there is a need in the art for protocols that define the topologyof a wireless mesh network in a highly dynamic mobile environment.

SUMMARY OF INVENTION

A method and system for determining a size of a local peer group (LPG)network in a dynamic roadway (mobile) environment is provided. In oneembodiment, the method comprises measuring a roundtrip time between afirst node and a second node, and utilizing the measured roundtrip timeto select the size of the local peer group network from a lookup table.In another embodiment, the method comprises determining when theroundtrip time exceeds a time interval of the heartbeat signal, and whenthe roundtrip time exceeds the time interval of the heartbeat signaladjusting the size of the local peer group network.

In one embodiment, the system comprises a processor operable to measurea roundtrip time between a first node and a second node and utilize themeasured roundtrip time to select the size of the local peer groupnetwork from a lookup table. In another embodiment, the processor isfurther operable to determine when the roundtrip time exceeds a timeinterval of the heartbeat signal, and when the roundtrip time exceedsthe time interval of the heartbeat signal adjusting the size of thelocal peer group network.

A computer readable medium embodying the method is also disclosed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an example of a local peer group (LPG) network;

FIG. 2 is a T_(R) model in accordance with one embodiment of theinvention;

FIG. 3 is an example of a look up table containing measured roundtriptime entries for controlling LPG size;

FIG. 4 is an example of a look up table containing measured roundtriptime entries and estimated roundtrip time entries for controlling LPGsize;

FIG. 5 is an example of a look up table for controlling LPG size;

FIG. 6 is a flow diagram of a method for decreasing LPG size by one;

FIG. 7 is a flow diagram of an alternative method for decreasing LPGsize; and

FIG. 8 is a computing environment that can benefit from the presentinvention.

DETAILED DESCRIPTION

A method and system for determining an optimal size of a local peergroup (LPG) network in a highly dynamic roadway (mobile) environment isprovided. A dynamic roadway (mobile) environment refers to the constantflow of automobiles along streets and highways, as well as the directionof movement by the automobiles. An LPG network refers to a mobile meshnetwork that provides for wireless communication between automobileswithin the network. The automobiles within the network are also known as“nodes”, and function in the same manner as nodes within a computernetwork. The invention is disclosed within the context of automobileswith radio transceivers functioning as the nodes within the LPG network.It is understood, however, that the invention and general concepts maybenefit any computer network.

FIG. 1 is an example of a topology of an LPG network. The topologycomprises several automobiles (nodes) each having a wireless transceiverlinked together to form the LPG network. The wireless transceiver may bepart of a larger computer system within each automobile. This computersystem is sometimes known as a “dashboard computer”. The dashboardcomputer comprises a memory and a processor and performs specificfunctions as directed by software stored within the memory. The wirelesstransceiver, which may be an 802.11 compliant transceiver and enablesthe automobiles and their respective dashboard computers to communicatewith each other.

One of the automobiles 102 within the topology is labeled GH (“GroupHeader”). The group header is the “head node” within the topology, orthe starting point from which the position of all the other automobiles(nodes) are measured. Automobiles 114 and 116 are one hop ahead ofautomobile (GH) 102. Automobiles 104 and 106 are one hop behindautomobile (GH) 102. Automobiles 108 and 110 are two hops behindautomobile (GH) 102. Automobile 112 is three hops behind automobile (GH)102. A hop is defined as the number of connections between nodesrequired to reach the group header 102. In instances where there is morethan one possible path to the group header, the smallest hop count isused to define the relative relationship between the nodes. For example,automobile 106 may communicate directly with the GH 102, or automobile106 may communicate with the GH 102 via automobile 104. When theautomobile 106 communicates directly with the GH 102, the hop countbetween these two automobiles is 1. When the automobile 106 communicatesindirectly with the GH 102 via automobile 104, the hop count betweenthese two automobiles is 2. If the GH 102 is presented with anautomobile that has one or more possible hop counts, e.g., automobile106, the GH 102 defines the relative position of that automobileaccording to the lowest hop count. Therefore, the relative positionbetween the GH 102 and automobile 106 is defined by a hop count of 1.

FIG. 2 is a T_(R) model in accordance with one embodiment of theinvention. T_(R) is the total reporting time necessary for a node torespond to a heartbeat message from a GH 102. T_(H) is the amount oftime it takes for the individual automobiles to receive the heartbeat(HB) message from the GH 102. T_(M) is the amount of time it takes forthe individual automobiles to send a message response (MR) to the GH102. T_(R) is equal to T_(H) plus T_(M). T_(R) is unique for eachautomobile. Generally, as the number of hops between an automobile andthe GH 102 increases, the time value for T_(R) also increases.

T_(R) may also be estimated as follows according to equation 1:

$\begin{matrix}\begin{matrix}{T_{R} = {T_{H} + T_{M}}} \\{= {d + {\left( {h - 1} \right){\overset{\_}{L}}_{H}} + {\left( {{2\frac{N}{h}} - 1} \right)d} + {\frac{N\left( {h + 1} \right)}{2}d^{\prime}}}} \\{= {{\left( {h - 1} \right)\frac{1 - {\left( {1 + \frac{N}{h}} \right)p^{\frac{N}{h}}} + {\frac{N}{h}p^{\frac{N}{h} + 1}}}{\left( {1 - p} \right)\left( {1 - p^{\frac{N}{h}}} \right)}d} + {2\frac{N}{h}d} + {\frac{N\left( {h + 1} \right)}{2}d^{\prime}}}}\end{matrix} & (1)\end{matrix}$Wherein the above equation, h is the hop count, N is the number of nodes(automobiles), d is the heartbeat transmittal duration, d′ is themessage response transmittal duration, and p is the probability oferror. L_(H) is the average per-hop HB forward latency, i.e., theaverage latency for the HB message to travel one hop; due to the randomaccess contention to use the wireless channel, the HB messageexperiences a random latency to be forwarded at each hop), which isgiven by equation 2:

$\begin{matrix}\begin{matrix}{{\overset{\_}{L}}_{H} = {{\frac{\left( {1 - p} \right)}{1 - p^{\frac{N}{h}}}d} + {\frac{\left( {1 - p} \right)p}{1 - p^{\frac{N}{h}}}2\; d} + {\frac{\left( {1 - p} \right)p^{2}}{1 - p^{\frac{N}{h}}}3d} + \ldots +}} \\{\frac{\left( {1 - p} \right)p^{\frac{N}{h} - 1}}{1 - p^{\frac{N}{h}}}\frac{N}{h}d} \\{= {\frac{\left( {1 - p} \right)d}{1 - p^{\frac{N}{h}}}\left\lbrack {1 + {2\; p} + {3\; p^{2}} + \ldots + {\frac{N}{h}p^{\frac{N}{h} - 1}}} \right\rbrack}} \\{= {\frac{1 - {\left( {1 + \frac{N}{h}} \right)p^{\frac{N}{h}}} + {\frac{N}{h}p^{\frac{N}{h} + 1}}}{\left( {1 - p} \right)\left( {1 - p^{\frac{N}{h}}} \right)}d}}\end{matrix} & (2)\end{matrix}$

A heartbeat is a periodic signal generated by the GH 102 and transmitted(broadcast) to the other automobiles to determine if these automobilesare still present within the LPG. The GH 102 sends out heartbeat signalsat regular intervals. Each automobile that receives the heartbeat signalrebroadcasts the heartbeat signal throughout the LPG. For example, asshown in FIG. 2, GH 102 broadcasts the heartbeat signal to automobile104; automobile 104 then rebroadcasts the heartbeat signal to automobile106. An automobile may remove itself from the LPG by roaming (driving)beyond the range of the heartbeat signal broadcast by GH 102 or by adriver turning off the automobile (which would also turn off thetransceiver that receives the heartbeat signal). Automobiles may beadded or removed to the LPG based upon their relative position (hopcount) to the GH 102. Upon receiving a heartbeat message from the GH102, an automobile responds with a message to the GH 102 acknowledgingthe heartbeat message. The acknowledgment indicates to the GH 102 thatthe responding automobile has received the heartbeat signal.

The heartbeat signal is a data packet that includes a “hop count” field.Every time the heartbeat signal is retransmitted, the hop count field isincreased by one. If the frequency of the heartbeat signal is too small,then the overhead associated with the heartbeat signal will exceed athreshold limit because the LPG size is updated too frequently. Thus,there is a need for a method to select a heartbeat frequency and an LPGsize in an efficient manner that does not over utilize system resources.

FIGS. 3 and 4 together demonstrate how a “lookup table” can be created.The lookup table can be used to select an appropriate LPG size. Eachtime entry within the lookup tables shown in FIG. 3 and FIG. 4 is givenin seconds. FIG. 3 is an incomplete lookup table created from observed(measured) message responses as described below. FIG. 4 is an estimatedlookup table based upon FIG. 3. The missing lookup table time entrieswithin FIG. 4 are calculated by a “least squares” approximation thatutilizes the measured time entries in the lookup table of FIG. 3. Theuse of a “least squares” approximation to calculate unknown values iswell known in the art.

The estimated time entries within lookup table 400 can be used to selectan appropriate LPG size. In one embodiment, the lookup table 400 iscreated by a simulator within the GH 102. The following example utilizesa QUALNET™ 3.8 simulator to create the lookup table 400. A GH 102broadcasts a heartbeat signal every 1000 milliseconds (1 second). Theheartbeat signal is broadcast in compliance with an 802.11a standard, ata data rate of 6 Mbps with an expected range of approximately 100meters. It is assumed that an automobile, e.g., automobile 104, receivesthe heartbeat signal within 300 milliseconds of the broadcast andresponds with a message response (MR) including a node identifier and ahop count. There may be instances where the automobile 104 cannotcommunicate with the GH 102 because the communication channel isunavailable or blocked. In these instances, the automobile 104 waits 10milliseconds, as a back off time period, and then attempts tocommunicate the MR to the GH 102.

Once the MR is communicated from the automobile 104 to the GH 102, theroundtrip time, T_(R), is calculated as discussed above and used topopulate lookup table 400. For example, a GH 102 broadcasts a heartbeatsignal to an automobile 104 and the automobile 104 sends anacknowledgment, i.e., a message response back to the GH 102. Furtherassume, for purposes of this example, that the automobile 104 is one hopaway from the GH 102 and that roundtrip time is 0.014 seconds. Alsoassume that a second automobile 108 is two hops away from the GH 102 andreturns a message response with a roundtrip time of 0.021 seconds. Athird automobile 106 is only one hop away, but returns a messageresponse with a roundtrip time of 0.024 seconds. These roundtrip timesare used to populate lookup table 300. Each roundtrip time is added tothe lookup table 300 and associated with the appropriate number of hops.As the number of hops increases from 1 to 10, the roundtrip time alsoincreases. An automobile may also be connected to the GH 102 by the samenumber of hops, but have a different roundtrip time. For example,automobiles 104 and 106 are both one hop away from the GH 102, but theroundtrip time associated with automobile 104 is less than the roundtriptime associated with automobile 106. The roundtrip times associated witha hop count increase from the smallest value to the greatest valuemoving from left to right across the lookup table 300.

Estimated values for each missing table entry are calculated from themeasured values in lookup table 300 utilizing the “least squares”approximation method. The use of approximation allows each entry inlookup table 400 to be completed. Lookup table 400 may then be used toselect an appropriate LPG size.

In one embodiment, an LPG size is selected based upon a maximum T_(R)value of 100 milliseconds (0.1 seconds). The T_(R) value ensures thedata passed between the automobile 104 and the GH 102 is “fresh” andrelevant. Freshness is important in a dynamic roadway environmentbecause it is desirable the GH 102 utilize only the most current data.An appropriate LPG size is selected from the lookup table 400 byselecting an LPG size associated with a time value less than 0.1 secondsand also constrained by the maximum number of hop counts. For example,if the maximum number of hop counts is set to five, then the selectedLPG size is forty. Forty is the selected LPG size because it correspondsto an entry on the lookup table 400 with a maximum value that does notexceed 0.1, i.e., 0.097 and the maximum number of hop counts. As long asthe automobile 104 is within five hop counts of the GH 102, and thereare forty or less automobiles within the LPG, the data passed betweenthe automobile 104 and the GH 102 will be received in less than 0.1seconds.

An important benefit of selecting an optimal LPG size from the lookuptable 400 is the reduction in computational overhead associated withmathematically calculating the LPG size. An additional benefit comesfrom selecting an LPG size that ensures T_(H) is greater than T_(R).When T_(R) is greater than T_(H), i.e., a second heartbeat signal istransmitted by the GH 102 before the MR is received. Any MRs received inresponse to the first heartbeat signal but after the second heartbeatsignal is transmitted may supply irrelevant or inaccurate information tothe GH 102. Therefore, it is important that the MRs received at the GH102 are in response to a heartbeat signal transmitted during thatparticular heartbeat cycle.

In one embodiment, the optimal LPG size is always associated with amaximum roundtrip time value less than a threshold value. As a GH 102moves through the dynamic roadway environment, the topology of the LPGmay constantly change as automobiles move in and out of communicationrange with the GH 102. When the topology changes frequently, thefrequency of the heartbeat signal is increased, i.e., the time intervalbetween heartbeat signals is shortened to maintain freshness of the LPG.When the topology does not change, for example, the GH 102 and thesurrounding automobiles are stopped at a red light or stalled intraffic, the frequency of the heartbeat signal is decreased, i.e., thetime interval between heartbeat signals is lengthened.

FIGS. 5, 6 and 7 collectively disclose a method for determining anoptimal LPG size. FIG. 5 is a flow diagram of a method for determiningan optimal LPG size. FIG. 6 is a flow diagram of a method fordetermining an appropriate hop count value that is utilized by themethod described by FIG. 5. FIG. 7 is an alternative method fordetermining an appropriate hop count value that is utilized by themethod described by FIG. 5.

The method starts at decision step 501 when a value for roundtrip timeis calculated. In one embodiment, the roundtrip time is calculated asdiscussed above according to equation 1. At decision step 502, adetermination is made as to whether a roundtrip time exceeds a heartbeattime interval. If the roundtrip time does not exceed the heartbeatinterval then the method proceeds to step 508. The current size of theLPG network as well as the current hop count value is known and storedat the automobile inside the dashboard computer. At step 508, themaximum hop count value is increased by 1. If the roundtrip time doesexceed the heartbeat interval, then the method proceeds to step 504.

At step 504, the hop count value is evaluated and decreased by one ofthree methods. Two of the three methods that can be used to evaluate thehop count at step 504 are illustrated in FIG. 6 and FIG. 7. In the thirdembodiment (not illustrated), the method utilizes a lookup table, suchas one shown in FIG. 4, to select an appropriate hop count value basedupon the roundtrip time as discussed above.

In the first embodiment, the hop count value is decreased by a valueof 1. Referring to FIG. 6, which is an enlarged view of the process thattakes place at step 504, at step 602 a downsizing request associatedwith the hop count value is received by the dashboard computer. Atdecision step 604, a determination is made as to whether the hop countvalue equals 1. If the hop count value equals 1, then the smallestpossible hop count value has already been reached and the method ends.If the hop count value is greater than 1, then the method proceeds tostep 606. At step 606, the hop count value is decreased by 1. The methodillustrated by FIGS. 5 and 6 together may be repeated to determine if anappropriate hop count value has been selected.

In another embodiment, the hop count value is factored, i.e., divided bya number to determine a new hop count value. Referring to FIG. 7, whichis an enlarged view of the process that takes place at step 504, at step702 a downsizing request associated with the hop count value is receivedby the dashboard computer. In one embodiment, the hop count value iscalculated as the midpoint value between the current hop count value anda lower bound value, such as zero. At step 704, a lower bound value isstored in a variable L. In one embodiment, the lower bound value is setto zero. An upper bound value, i.e., the current hop count value (h), isstored in a variable R. The current hop count value (h) is divided by afactor, .e.g., 2, and the computed value is stored in variable x. Forexample, if the current hop count value is 10, and the value of thefactor is 2, then 10 is divided by 2 to compute a value of 5. The value5 is stored in the variable x. At step 706, the roundtrip time isrecalculated based upon the hop count value stored in the variable x.The roundtrip time calculated at step 706 should be less than theroundtrip time calculated at step 501 because the hop count value hasdecreased.

At decision step 708, a determination is made as to whether theroundtrip time is now smaller than a threshold value, i.e., theheartbeat interval. If the roundtrip time is not smaller than thethreshold value, the method proceeds to step 710. At step 710, thecurrent hop count value stored in the variable x is also stored in thevariable y. The hop count value stored in x is also restored into thevariable R as the value of a new upper bound. Then the hop count valuestored in the variable x is factored again. In one embodiment, a new hopcount value is calculated according to the equation: x=[(R−L)/2] whichprovides a new midpoint value between the lower bound and the upperbound. The method then proceeds to decision step 714, where adetermination is made as to whether L<x<R. If L<x<R is true, then themethod proceeds to step 716 and the hop count value is set to the valuestored in the variable x. If L<x<R is false, then the method loops backto step 706.

The following example illustrates how a hop count value of 10 may bereset to a hop count value of 3 by the method shown in FIG. 7. The hopcount value stored in variable h is also stored in the variable R. R isthe upper bound. The lower bound is set to zero and stored in thevariable L. A new hop count value is computed as the value of themidpoint between the upper bound and the lower bound according to theequation x=[(R−L)/2]. After substituting in the values of the presentvariables, the equation may be rewritten as x=[(10−0)/2]=5. A newroundtrip time is calculated based upon a maximum hop count value of 5.However, a hop count value of 5, in this example, results in a roundtriptime that exceeds a threshold value, i.e., the heartbeat time interval.The current hop count value, 5, is refactored. The current hop countvalue 5 becomes the new upper bound, and L is still the lower bound. Anew midpoint between the upper bound and the lower bound isrecalculated. In the present example, the midpoint between the upperbound (R) and the lower bound (L) is calculated according to theequation x=[(R−L)/2]. After substituting in the values of the presentvariables, the equation may be rewritten as x=[(5−0)/2]=2.5. In oneembodiment, when a non-whole number is computed as a value of a hopcount, the number is rounded up. Therefore, 2.5 is rounded up to 3. Adetermination is then made as to whether the calculated hop count value,e.g., 3, is within the range of the lower bound and the upper bound. Inthe present example, the hop count value 3 is greater than the lowerbound value of 0 and less than the upper bound value of 5. The new hopcount value is set to 3 and used to compute a new roundtrip time.

Referring back to decision step 708, if the roundtrip time is smallerthan the threshold value, the method proceeds to step 712. At step 712,the value within the variable x is first stored in the variable y.Recall that the variable x stores the computed midpoint value betweenthe upper bound and the lower bound of the original hop count value. Thevalue stored in the variable x is then stored in the variable L.Finally, the value of the variable x is recomputed according to theequation x=L+[(R−L)/2]. As an example, assume that at step 704, L is setequal to 0, h is set equal to 10, R is set equal to h, and x iscalculated according to the equation x=[(R−L)/2] and found to have avalue equal to 5. At step 712, y=5, L=5, and x is recalculated accordingto the x=L+[(R−L)/2]. Substituting in the known values for each of thevariables provides the equation x=5+[(10−5)/2] which gives a resultx=7.5.

The method then proceeds on to step 714. Again, using the resultscomputed in the example from step 712, a determination is made as towhether L<x<R is true. Substituting in the values for L, x, and R fromstep 712, 5<7.5<10, which results in a true result, i.e., x lies betweenthe lower bound and the upper bound. In one embodiment, the hop countvalue is rounded up from 7.5 to 8 because a hop count value must be awhole number. The method then loops back to step 706, and the roundtriptime is calculated based upon the value of x.

FIG. 8 is an example of a computing environment that can benefit fromthe present invention. In one embodiment, the computing environmentcomprises a GH 102 wirelessly in communication with another automobile104. The GH 102 and automobile 104 collectively form an LPG network. Adashboard computer 802 within the GH 102 controls the size of the LPGnetwork and communication between the GH 102 and the automobile 104. Itis understood that the automobile 104 has a similar dashboard computer(not shown) capable of receiving and responding to communicationsreceived from the GH 102.

The dashboard computer 802 comprises a processor (CPU) 804, atransceiver 806, and a memory 808. The computer 802 is coupled to thetransceiver 806 and the memory 808 and executes programs stored inmemory such as “HB cycle control” 814 and “awareness components” 810.The transceiver 806 enables wireless (RF) communication between the GH102 and the automobile 104. In one embodiment, the GH 102 communicateswith the automobile 104 via the 802.11a standard. It is understood thatthe invention may use any wireless communication standard. Othercomponents commonly found within a dashboard computer 802, such as apower source, an antenna, a storage unit, and various support circuitryare understood to be present, but not shown in FIG. 8.

The memory 808 may include random access memory, read only memory,removable disk memory, flash memory, and various combinations of thesetypes of memory. The memory 808 is sometimes referred to as a mainmemory and may in part be used as cache memory. The memory 808 stores atleast the “awareness components” 810, an LPG lookup table 812, and the“HB cycle control” 814. The awareness components 810 store the size ofthe LPG network and maintain a list of all the vehicles or automobileswithin the LPG network. The awareness components 810 may also maintaininformation associated with each automobile within the LPG network. Anexample of the LPG lookup table 814 is provided in FIG. 4. The LPGlookup table 814 enables selection of an optimal LPG network size basedupon the roundtrip time.

The “HB cycle control” 814 controls the maximum allowable hop countvalue between the GH 102 and the automobile 104. The function of the “HBcycle control” 814 is described above in regards to FIGS. 5, 6 and 7. Inone embodiment, the “HB cycle control” 814 increases the hop count valuewhen the roundtrip time is less than the heartbeat time interval. Inanother embodiment, the “HB cycle control” 814 decreases the hop countvalue when the roundtrip time is greater than the heartbeat timeinterval. Specific methods for decreasing the hop count value aredescribed in regards to FIGS. 6 and 7. The “HB cycle control” 814 mayalso select an optimal LPG network size by utilizing a lookup table suchas the one shown in FIG. 4.

While the present invention has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present invention. It is therefore intended that the presentinvention not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

1. A computer implemented method for determining a size of a local peergroup network, comprising: measuring a roundtrip time between a firstnode and a second node; utilizing the measured roundtrip time to selectthe size of the local peer group network from a lookup table, whereinthe computer performs one or more steps of measuring and utilizing;transmitting a heartbeat signal from the first node to the second node;receiving the heartbeat signal at the second node; and transmitting amessage response from the second node to the first node in response toreceiving the heartbeat signal, wherein the message response comprises anode identifier and a hop count value and the roundtrip time isassociated with the hop count value in the lookup table.
 2. The methodof claim 1, further comprising: populating the lookup table with theroundtrip time; estimating one or more additional roundtrip times fromthe roundtrip time; and completing the lookup table with the one or moreadditional roundtrip times.
 3. A computer implemented method fordetermining a size of a local peer group network, comprising: measuringa roundtrip time between a first node and a second node; and utilizingthe measured roundtrip time to select the size of the local peer groupnetwork from a lookup table, wherein the computer performs one or moresteps of measuring and utilizing; when the roundtrip time exceeds thetime interval of a heartbeat signal, adjusting the size of the localpeer group network.
 4. The method of claim 3, further comprising:selecting a new size for the local peer group network from the lookuptable by utilizing the roundtrip time that exceeds the time interval ofthe heartbeat signal.
 5. The method of claim 3, further comprising:decreasing a maximum allowable hop count value between the first nodeand the second node; when the roundtrip time continues to exceed thetime interval of the heartbeat signal, further decreasing the maximumallowable hop count value between the first node and the second nodeuntil the roundtrip time between the first node and the second node doesnot exceed the time interval of the heartbeat signal.
 6. The method ofclaim 3, further comprising: dividing a maximum allowable hop countvalue by a factor to establish a new maximum allowable hop count valuebetween the first node and the second node; when the roundtrip timecontinues to exceed the time interval of the heartbeat signal, furtherdividing the new maximum allowable hop count value by the factor untilthe roundtrip time between the first node and the second node does notexceed the time interval of the heartbeat signal.
 7. A computer programproduct for determining a size of a local peer group network,comprising: a storage device readable by a processor and storinginstructions for execution by the processor for performing a methodcomprising: measuring a roundtrip time between a first node and a secondnode; utilizing the measured roundtrip time to select the size of thelocal peer group network from a lookup table, wherein the computerperforms one or more steps of measuring and utilizing; transmitting aheartbeat signal from the first node to the second node; receiving theheartbeat signal at the second node; and transmitting a message responsefrom the second node to the first node in response to receiving theheartbeat signal, wherein the message response comprises a nodeidentifier and a hop count value and the roundtrip time is associatedwith the hop count value in the lookup table.
 8. The computer programproduct of claim 7, further comprising: populating the lookup table withthe roundtrip time; estimating one or more additional roundtrip timesfrom the roundtrip time; and completing the lookup table with the one ormore additional roundtrip times.
 9. A computer program product fordetermining a size of a local peer group network, comprising: a storagedevice readable by a processor and storing instructions for execution bythe processor for performing a method comprising: measuring a roundtriptime between a first node and a second node; and utilizing the measuredroundtrip time to select the size of the local peer group network from alookup table, wherein the computer performs one or more steps ofmeasuring and utilizing; when the roundtrip time exceeds a time intervalof a heartbeat signal, adjusting the size of the local peer groupnetwork.
 10. The computer program product of claim 9, furthercomprising: selecting a new size for the local peer group network fromthe lookup table by utilizing the roundtrip time that exceeds the timeinterval of the heartbeat signal.
 11. The computer program product ofclaim 9, further comprising: decreasing a maximum allowable hop countvalue between the first node and the second node; when the roundtriptime continues to exceed the time interval of the heartbeat signal,further decreasing the maximum allowable hop count value between thefirst node and the second node until the roundtrip time between thefirst node and the second node does not exceed the time interval of theheartbeat signal.
 12. The computer program product of claim 9, furthercomprising: dividing a maximum allowable hop count value by a factor toestablish a new maximum allowable hop count value between the first nodeand the second node; when the roundtrip time continues to exceed thetime interval of the heartbeat signal, further dividing the new maximumallowable hop count value by the factor until the roundtrip time betweenthe first node and the second node does not exceed the time interval ofthe heartbeat signal.
 13. A system for determining a size of a localpeer group network, comprising: a processor operable to measure aroundtrip time between a first node and a second node and utilize themeasured roundtrip time to select the size of the local peer groupnetwork from a lookup table; wherein the processor is further operableto transmit a heartbeat signal from the first node to the second node,receive the heartbeat signal at the second node, and transmit a messageresponse from the second node to the first node in response to receivingthe heartbeat signal, wherein the message response comprises a nodeidentifier and a hop count value and the roundtrip time is associatedwith the hop count value in the lookup table.
 14. The system of claim13, wherein the processor is further operable to populate the lookuptable with the roundtrip time estimate one or more additional roundtriptimes from the roundtrip time, and complete the lookup table with theone or more additional roundtrip times.
 15. A system for determining asize of a local peer group network, comprising: a processor operable tomeasure a roundtrip time between a first node and a second node andutilize the measured roundtrip time to select the size of the local peergroup network from a lookup table; wherein the processor is furtheroperable to determine when the roundtrip time exceeds a time interval ofa heartbeat signal, and when the roundtrip time exceeds the timeinterval of the heartbeat signal adjust the size of the local peer groupnetwork.
 16. The system of claim 15, wherein the processor is furtheroperable to select a new size for the local peer group network from thelookup table by utilizing the roundtrip time that exceeds the timeinterval of the heartbeat signal.
 17. The system of claim 15, whereinthe processor is further operable to decrease a maximum allowable hopcount value between the first node and the second node and determine ifthe roundtrip time between the first node and the second node continuesto exceed the time interval of the heartbeat signal, and when theroundtrip time continues to exceed the time interval of the heartbeatsignal, further decrease the maximum allowable hop count value betweenthe first node and the second node until the roundtrip time between thefirst node and the second node does not exceed the time interval of theheartbeat signal.
 18. The system of claim 15, wherein the processor isfurther operable to divide a maximum allowable hop count value by afactor to establish a new maximum allowable hop count value between thefirst node and the second node, determine if the roundtrip time betweenthe first node and the second node continues to exceed the time intervalof the heartbeat signal, and if the roundtrip time continues to exceedthe time interval of the heartbeat signal, further divide the newmaximum allowable hop count value by the factor until the roundtrip timebetween the first node and the second node does not exceed the timeinterval of the heartbeat signal.